Previous studies have shown that one can exploit “wisdom of crowds” by oneself. This is achieved by aggregating multiple “quasi-independent” estimates from the same person. However, previous methods were not necessarily easy to utilize. Therefore, we propose an efficient method based on perspective-taking. The procedure is as follows: First, one makes her/his own estimation. Second, one estimates again based on a different perspective (“general public”). Then these two estimations were averaged. Two experiments revealed that our method effectively induced the wisdom of crowds by oneself. More importantly, participants in our method made estimations more quickly than those in a previously proposed method, suggesting that our method required a relatively diminished cognitive load for participants. Further investigation suggested that our method was immune to adverse effects of confidence. Therefore, the present findings show that our method could be effective and efficient method for inducing the wisdom of crowds in one mind.